update-manager output is inscrutable when phased-updates across 2 separate source packages prevent installation (grub2 vs grub2-signed)

[Steve Langasek]

There is a grub2+grub2-signed SRU in eoan-updates that is failing to install here. The publication all looks correct, and 'apt upgrade' or 'apt dist-upgrade' show no problems, but update-manager repeatedly shows:

"Package dependencies cannot be resolved
This error could be caused by required additional software packages which are missing or not installable. Furthermore there could be a conflict between software packages which are not allowed to be installed at the same time.
Transaction failed: Package dependencies cannot be resolved
 The following packages have unmet dependencies:

grub-efi-amd64-signed:"

Dependencies of the current eoan-updates version of the package are:

Depends: grub-efi-amd64-bin (= 2.04-1ubuntu12.2), grub-efi-amd64 | grub-pc

I have grub-pc and grub-efi-amd64-bin installed, and they should both be installable.

[Steve Langasek (vorlon)]

Ok, running update-manager --debug shows me that:

INFO:root:holding back phased update grub-common (60 < 72)
INFO:root:holding back phased update grub-efi-amd64-bin (60 < 72)
INFO:root:holding back phased update grub-pc (60 < 72)
INFO:root:holding back phased update grub-pc-bin (60 < 72)
INFO:root:holding back phased update grub2-common (60 < 72)

So this is very confusing output in the case of a phased update involving two different source packages.